The present invention claims the benefit of Korean Patent Application No. P2000-45942 filed in Korea on Aug. 8, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an electrostatic damage preventing apparatus for a liquid crystal display.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls light transmissivity of liquid crystal cells in response to a video signal, thereby displaying an image. An active matrix LCD provided with a switching device for each liquid crystal cell is suitable for displaying moving images. A thin film transistor (TFT) is generally used as the switching device.
An active matrix LCD displays images corresponding to input video signals. Each pixel of the active matrix LCD includes a liquid crystal cell that controls the quantity of transmitted light according to a data signal voltage level input from the data line. A TFT is arranged at each intersection between gate lines and data lines. The data line will switch a data signal delivered to the liquid crystal cell in response to a scanning signal (i.e., a gate signal) from the gate line.
In an active matrix LCD as shown in FIG. 1, an electrostatic damage preventing apparatus, hereinafter referred briefly to as xe2x80x9cESD preventing apparatus,xe2x80x9d for protecting a liquid crystal display panel from static electricity produced during the cutting of the substrate is provided at the liquid crystal display panel.
Referring to FIG. 1, the conventional ESD preventing apparatus includes a plurality of switching devices for ESD prevention that are provided on a TFT array 13 of a liquid crystal display panel 1. The TFT array 13 has liquid crystal cells that respond to an electric field in order to control a quantity of transmitted light and thin film transistors (TFT""s) 4 that respond to gate signals on gate lines 2 to selectively connect data lines 3 to liquid crystal cells 5. The ends of the gate line 2 and the data line 3 are provided with pads 8 and 9, respectively. The pad 8 provided at the end of the gate line 2 receives a gate signal from a gate driver (not shown) while the pad 9 provided at the end of the data line 4 receives a data signal from a data driver (not shown).
The ESD preventing apparatus further includes a ground voltage line 16 provided at an outer side of the liquid crystal display panel 1, a horizontal ground voltage line 17 that extends from the ground voltage line 16 in parallel to the TFT array 13, and a vertical ground voltage line 18 that is perpendicular to the TFT array 13. A first ESD-preventing switching device 10 is connected between the ground voltage line 16 and the horizontal ground voltage line 17, thereby preventing an electrostatic discharge voltage generated from pad 6 from being delivered into a fifth ESD-preventing switching device group 15 over the ground voltage line 16.
A second ESD-preventing switching device group 14 has two parallel switching devices connected between the ground voltage line 16 and the vertical ground voltage line 18, thereby diverting an electrostatic discharge voltage applied over the vertical ground voltage line 18.
A third ESD-preventing switching device group 19 is connected between the gate line 2 and the vertical ground voltage line 18, thereby diverting an electrostatic voltage by the second ESD-preventing switching device group 14 to prevent the electrostatic voltage from being directly applied to the TFT array 13.
A fourth ESD-preventing switching device group 20 is connected between the gate pad 8 and the gate line 2, thereby diverting an electrostatic voltage on the gate line 2 to prevent the electrostatic voltage from the gate pad 8 from being directly applied to the TFT array 13.
A fifth ESD-preventing switching device group 15 is connected between the horizontal ground voltage line 17 and the TFT array 13, thereby allowing a voltage on the horizontal ground voltage line 17 to be approximately equal to a voltage on the data line 3.
A sixth ESD-preventing switching device group 22 is connected between a low gate voltage line 7 and the gate line 2, thereby allowing a voltage on the gate line 2 to be diverted by the fourth ESD-preventing switching device group 20 to be approximately equal to a voltage on the low gate voltage line 7.
A seventh ESD-preventing switching device group 21 is connected between a common voltage pad Vcom and the horizontal ground voltage line 17, thereby diverting an electrostatic voltage applied via the common voltage pad Vcom.
In FIG. 1, the first to seventh ESD-preventing switching device groups 10, 14, 19, 20, 15, 22 and 21 prevent damage to the TFT array 13 caused by an electrostatic voltage applied, via the ground voltage line 16, to the gate line 2 or the data line 3. Accordingly, the first ESD-preventing switching device 10 includes first and second TFT""s 11 and 12 each having drain electrodes 11a and 12a and gate electrodes 11b and 12b respectively connected to each other. A source electrode 11c of the first TFT 11 and the drain electrode 12a of the second TFT 12 are connected to the horizontal ground voltage line 17, and the drain electrode 11a of the first TFT 11 and a source electrode 12c of the second TFT 12 are connected to the horizontal voltage line 17 that is disposed perpendicular to the ground voltage line 16.
Meanwhile, the second, third, fourth and sixth ESD-preventing switching devices 14, 19, 20 and 22 have similar configurations to provide the similar functions.
The conventional ESD preventing apparatus for the LCD has problematic in that, if excessive static electricity is supplied to the pad 6, insulation breakage of the first ESD-preventing switching device 10 occurs. Similarly, if an excessive electrostatic voltage is applied to the seventh ESD-preventing switching device 21 that is connected in series between the common voltage pad Vcom and the horizontal ground voltage line 17, insulation breakdown of the seventh ESD-preventing switching device 21 may occur. Accordingly, if the first and seventh ESD-preventing switching devices 10 and 21 undergo insulation breakage, then a large electrostatic voltage is applied to the TFT array 13, thereby causing insulation breakage of the TFT 4.
Accordingly, the present invention is directed to an electrostatic damage preventing apparatus that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an electrostatic damage preventing apparatus for a liquid crystal display that is capable of preventing insulation breakage or device damage through a single switching device connected in series to an external line of a thin film transistor array.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an electrostatic damage preventing apparatus for a thin film transistor array of a liquid crystal display includes a horizontal ground voltage line disposed at a first perimeter portion of the thin film array, a vertical ground voltage line disposed at a second perimeter portion of the thin film transistor array, and a first electrostatic damage-preventing switching device group including parallel connection of at least two electrostatic damage-preventing switching devices to divide and divert an electrostatic voltage applied over the horizontal ground voltage line.
In another aspect, an electrostatic damage preventing apparatus for a liquid crystal display includes a horizontal ground voltage line and a vertical ground voltage line arranged at an outer perimeter of a thin film transistor array, a first electrostatic damage-preventing switching device group including parallel connection of at least two electrostatic damage-preventing switching devices to divide and divert an electrostatic voltage applied over the horizontal ground voltage line, and a second electrostatic damage-preventing switching device group including parallel connection of at least two electrostatic damage-preventing switching devices to divide and divert an electrostatic voltage applied over a common voltage line.
In another aspect, a method of preventing electrostatic damage to a liquid crystal display includes the steps of dividing and diverting an electrostatic voltage applied over a horizontal ground voltage line, and dividing and diverting an electrostatic voltage applied over a common voltage line.
In another aspect, a liquid crystal display device includes a thin film transistor array, a plurality of gate lines disposed in a first direction and connected to the thin film transistors, a plurality of data lines disposed in a second direction perpendicular to the first direction and connected to the thin film transistors, a horizontal ground voltage line disposed at a first perimeter portion of the thin film transistor array, a vertical ground voltage line disposed at a second perimeter portion of the thin film transistor array, and a first electrostatic damage-preventing switching device group including parallel connection of at least two electrostatic damage-preventing switching devices to divide and divert an electrostatic voltage applied over the horizontal ground voltage line.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.